Abstract: With rapeseed fields having been reclaimed from alpine meadow for 0, 10, 20 and 30 years at the Haibei Research Station, Chinese Academy of Sciences as test objects, this paper studied the changes of soil organic carbon (SOC) and its fractions including light fraction organic carbon (LFOC) and heavy fraction organic carbon (HFOC) in 0～10, 10～20, 20～30 and 30～40 cm soil layers with reclamation duration. The results showed that after the alpine meadow reclaimed, the changes of SOC and its fractions mainly occurred in 0～10 cm soil layer, with LFOC decreased most rapidly and followed by HFOC and SOC. After the conversion from alpine meadow to cropland for 30 years, the SOC, LFOC and HFOC in 0～10 soil layer decreased by 37.64%, 48.63% and 43.97%, and their decrement in 0～40 cm soil layer was 785.77, 16.79 and 460.29 kg C·hm^-2·yr^-1, respectively. The storage of soil carbon pool was decreased from 143 516.94 to 114 298.34 kg C·hm^-2·yr^-1. Reclamation made alpine meadow as a carbon sink turn into a carbon source.

Key words: Woody plant, Sprouting, Disturbance, Persistence niche